1. Field of the Invention
The present invention relates to a character generating method and apparatus for developing an outline character, expressed by a logical coordinate system, on physical coordinates expressed by integer values.
2. Description of the Related Art
A printer, a display device or the like requires that character patterns be generated to print or display characters. In the generation of character patterns, recently, characters of various character sizes are demanded even for the same character. Therefore, the memory capacity increases if characters of various character sizes are given for the same character, particularly, for Kanji characters or the like which have many types of characters.
As a solution to this problem, an outline font system has been proposed. According to this system, data of character patterns whose contour lines are expressed in real numbers and also by a logical coordinate system, is provided, and this data is converted to a designated character size coordinate system to develop characters to a bit map image expressed by integer values.
It is demanded that characters should be restored to the original designs with high fidelity even after enlargement or reduction.
FIGS. 11A, 11B, 12A and 12B are explanatory diagrams of prior art.
Conventionally, in developing logical coordinate data expressed by real numbers, such as a figure or an outline font, to a bit map image expressed by integer values, a fractional portion of character data is rounded so that the data will be expressed in the units of pixels of a printer or a display. In order to express coordinate data by closest pixels, rounding is typically performed to count fractions of 5 and over as a whole number.
For example, individual contour points which constitute a Mincho Kanji character "Ichi" (meaning "one") expressed in an outline form as shown in FIG. 11A, are stored by integer logical coordinates like 1000.times.1000. Character outline data on the logical coordinates are converted to the necessary character size to have coordinate values including decimal points. If all the points are rounded to express the coordinate values by physical coordinates, all the points will be rounded to the nearest whole numbers.
For example, the character "Ichi" in FIG. 11A is a horizontal stroke and is broken down into a stroking start portion, a stroking sustain portion and a stroking end portion. In this case, the stroking start portion on the left end of the character "Ichi" in FIG. 11A is converted into coordinates as shown in FIG. 11B if it is reduced to a character size of 50.times.50 dots. This stroking start portion consists of six points a, b, c, f, e and d in the clockwise direction. To reduce those six points in the 50.times.50 character size, the point a is converted through the reduction process to coordinate values X=2.4, Y=27.6, which contain fractions.
To round all the points to integers so that they can be expressed by physical coordinates, those points are rounded to the nearest integers as shown in FIG. 12A. For example, the contour point a is rounded to coordinate values of X=2, Y=28. The rounded contour points are then developed into a dot-based bit map image as shown in FIG. 12B.
For the illustrated pattern of the Kanji character "Ichi" whose stroking start portion on the left end has a triangular portion protruding or extending downward, this extending portion is expressed by one pixel in a reduced character. The same applies to the extending portion of the stroking end portion of a vertical stroke or the stroking start portion and stroking end portion of an oblique stroke.
According to the prior art, however, after the outline coordinates are reduced or enlarged and then rounded, the triangular extending portion of the stroking start portion of a horizontal stroke or the extending portion of a vertical stroke appears protruding by one pixel. Therefore, the bit map image of the character which is developed on the physical coordinates would appear significantly different from the original image and would be too emphasized, thus deteriorating the character quality. This tendency is prominent particularly for characters of a small size.